Q4) (2 points) The local grocery store consists of two cashiers. The customers arrive according to a Poisson distribution and the service times are based on a negative exponential distribution. The average customer service time is 5 minutes and the average time between the arrivals of successive customers is 3 minutes. a- What is the average number of customers waiting in each line at the checkout counter? b- How much time is a customer expected to spend at the grocery store